1. Field of the Invention
The present invention relates to a system for controlling braking effect to slow or stop motor vehicles.
2. Description of the Related Art
Attempts have heretofore been made to adjust a braking force in response to braking operation to improve the braking effect of a motor vehicle. Japanese patent publication Nos. 21982/90 and 46426/90, for example, disclose that a motor vehicle is decelerated in response to braking operation when the brake is applied. The prior art systems control a booster provided between a brake pedal and a master cylinder to assist in applying pressure to the brake pedal.
However, when the booster is controlled, reaction force is applied to the brake pedal. This deteriorates the brake feeling of a driver.
To this end, simulation means may be included to maintain the brake feeling when wheel cylinder pressure is adjusted. The simulation means is connected between the master cylinder and the wheel cylinder so as to vary the volume of the master cylinder in response to output pressure of the master cylinder and adjust pressure of the wheel cylinder in response to pedal pressure when the brake is applied. The simulation means controls wheel cylinder pressure in response to pedal pressure when the brake is applied. At that time, the master cylinder is disconnected from the wheel cylinder not only to control of the wheel cylinder simply in response to the pedal pressure, but also to effect anti-skid brake control in response to the speed of rotation of the wheels. In addition, when the pressure in the master cylinder is increased, the volume of a chamber communicated with the master cylinder is increased to ensure better brake feeling.
In order to control pressure of the wheel cylinder, the simulation control means typically includes a pump, an accumulator for accumulating output pressure from the pump, a reservoir, and a linear pressure control valve selectively connected to the accumulator and the reservoir so as to feed a predetermined pressure to the wheel cylinder. This type of means, however, requires frequent operation of the linear pressure control valve. Also, the pump needs be frequently operated in the event of a frequent leak in the linear pressure control valve.
Accordingly, it is an object of the present invention to provide a brake control system which includes simulation control means and allows for less frequent operation of a pressure control means.